I went ahead and sanded the birch door interior, then applied the stain, and finished with 1 coat of polyurethane.

I will apply two more coats of poly later, but I wanted one coat on before I appled the trim molding. Once dried I installed the window.

Note the window opening needs trimming out. I intend to use aluminum stock to complete the interior trim around the window. More on that later....
Preparing the Door Interior